The present invention relates generally to a method for making drumsticks and more specifically to a method for controlling the density of drumsticks during the manufacturing process.
Drumsticks have traditionally been made of wood. Although wood is familiar to everyone, it has some disadvantages. A particular disadvantage is its fragilityxe2x80x94it is possible for a drummer to break his drumsticks during a performance. Wood is also not completely reproducible. Several attempts have been made to replace wood with plastic. These have typically involved conventional casting or extrusion, with final machining to shapexe2x80x94not too dissimilar to how wood is handled. However, the resulting plastic products are heavy (compared to wood), are prone to warp, usually differ in timber, texture or other variables, and are relatively expensive. Another technology that involves internally foaming plastics has potential for use in making plastic drumsticks. Traditional foaming technologies produce the familiar polystyrene and polyurethane foams, which are good insulators but have little strength. Newer foaming technology can produce much smaller bubbles, and the materials can retain much or all of the impact strength of the underlying plastic while being lighter (less dense). Such techniques are described in, for example, WO 90/07546; WO 98/08667; or WO 98/31521.
In the present system, selected plastics and fillers are melted in an extruder and a pressurized gas such as nitrogen or carbon dioxide is incorporated into the molten polymer. Extruders are well known in the art and basically comprise a barrel or tube that applies electrical heat to the polymer and a screw or auger that turns at a given rate to feed the material into the mold. The screw also applies frictional heat to the polymer.
A gate, or shut-off nozzle, is provided at one end of the barrel for release of the contained substance and a screw or plunger is provided at the opposite end for forcing the contained substance out of the shut-off nozzle. The shut-off nozzle of the extruder empties into a cavity in the mold that has a cooling system and that is in the shape of a drumstick. The mold is further provided with vents that allow the air, already in the mold, to escape upon injection of the gas-polymer mixture. When a specified amount of the gas-polymer mixture is injected into the mold, internal foaming and cooling of the mixture occurs. The amount of internal foaming that takes place is related to the amount of polymer that is injected into the cavity of the mold. By controlling the injection speed and the mold temperature, the final density and bubble size is controlled. In the present system, a very high density of nucleation sites can be achieved. After cooling is complete a drumstick can be removed from the mold and is ready for use.
An improved drumstick made from plastic, wherein the plastic is internally foamed sufficiently to give the plastic drumstick a density and resilience similar to wood and having greater impact strength than wood. The improved drumstick is made by an injection molding process that imparts a micro-foamed structure to the drumstick. The resulting drumstick provides a livelier rebound off a drum head than wooden drumsticks and a higher quality ringing sound when playing a cymbal, than previous plastic and wooden drumsticks. Further, the present drumstick lasts approximately five times as long as wooden drumsticks and can be made in various colors and even be made to glow in the dark.